Redox Effector Factor-1, Combined with Reactive Oxygen Species, Plays an Important Role in the Transformation of JB6 Cells

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Apurinic/apyrimidinic endonuclease/redox effector factor-1 (APE/Ref-1) is a multifunctional protein involved both in DNA base excision repair and redox regulation. Studies have suggested that abnormal Ref-1 levels and/or activities are associated with tumor progression and sensitivities to treatment, but no direct evidence has yet been published regarding the role of Ref-1 in malignant transformation. We utilized the well-documented tumor promotor-sensitive JB6 mouse epithelial cell model as well as new transformants [by ultraviolet light B (UVB), H 2 O 2 or Cd] to study this phenomenon.

Significant increases of reactive oxygen species (ROS) were observed in JB6P+ and all the transformants compared with promotor-resistant JB6P− cells. These increases were paralleled by a sustained elevation of Ref-1 expression. Further analysis exhibited a strong inverse correlation between oxidative DNA lesions [8-oxodeoxyguanosine (8-oxo-dG)] and Ref-1 levels in all JB6 cells. Notably, apoptosis occurred after knock-down of Ref-1 by small interfering RNA (siRNA)] demonstrated by a ∼ 2-fold increase of Annexin V-positive JB6P+ cells. Ref-1 depletion also inhibited 12- O -tetradecanoylphorbol-13-acetate (TPA)-induced anchorage-independent growth of JB6P+ by 40% and reduced the colony numbers of JB6P+/H 2 O 2 and JB6P+/Cd cells. Mechanistic studies revealed that Ref-1 reduction was associated with an increase of intracellular ROS levels and a marked decrease of activator protein-1 (AP-1) transcription activities in JB6P+/H 2 O 2 cells.

This is the first report of the novel role of Ref-1 in cellular transformation. Based on the data presented here, we propose that induction of Ref-1, serving as an adaptive response to elevated ROS, plays a critical role in transformation and protects cells from excess ROS stresses through both DNA repair and activation of transcription factors such as activator protein-1.


This article was originally published in Carcinogenesis, volume 28, issue 11, in 2007. DOI: 10.1093/carcin/bgm128


Oxford University Press